The overall objective of the work is to advance the knowledge of the hydrodynamic and some other structural parameters which determine the behavior of single-stranded DNA, various forms of duplex DNA, and discrete complexes of DNA with histones. Kinetic and equilibrium ultracentrifugation techniques and gel electrophoresis methods will be the major techniques employed. Specific projects to be carried out include: 1) measurements of the sedimentation coefficients of nucleohistone complexes made in the laboratory between four of the cellular histones and various forms of bacteriophage PM2 DNA (linear, nicked circular, and closed circular DNA), so that hydrodynamic modeling of these complexes can be attempted; 2) measurement of the Kuhn statistical length and excluded volume parameter for single-stranded DNA at neutral pH under conditions where the hydrodynamic behavior of the DNA is amenable to treatment with an existing theory; 3) measurement of the excluded volume parameter through a new method developed in connection with this research; 4) measurement of the hydrodynamic and some other properties of "figure-8" molecules which are to be produced in this laboratory; these studies may lead to new methods for assessing the rotation angle of the DNA helix and the nature of random fluctuations about the sites of nicks in the DNA helix; 5) studies as to the nature of the finite number of unique sites in supercoiled PM2 closed circular DNA which preliminary work has shown are attacked by a highly single strand-specific nuclease isolated in this laboratory, and studies to ascertain whether these sites can be identified with sites of initiation of transcription; 6) further studies as to the nature of the process leading to irreversible denaturation in closed circular PM2 DNA, which appears to be distinct from the behavior of other closed circular DNA's in this regard.